A conventional foot pedal hammer seat is used for clamping a bass drum as shown in FIGS. 1, 2 and 3. It mainly includes a hammer seat 1a placed on the floor with a base board 2a at the front side thereof, and a pair of rack stands 3a at the left and right sides of the base board 2a having the top to jointly hinge an axle 4a. The axle 4a runs through a hub 5a which has one side fastened to a hammer 6a. The hammer seat 1a has a rear side hinged a pedal 7a. The pedal 7a has a front side fastened to one end of a chain 8a. The pedal 7a also has a front end higher than a rear end in an inclined manner. The chain 8a has another end fastened to the hub 5a. A clamping means 9a is hinged on the base board 2a. The clamping means 9a is run through in the middle by a transverse axle 10a to be hinged on the base board 2a. The clamping means 9a further has a pressing jaw 11a transversely hinged at the front side above the base board 2a to jointly clamp a drum rim a of the bass drum. The clamping means 9a further has a screw hole at the rear side screwed by a pressing bolt 12a with a distal end butting the upper side of the base board 2a. 
The pedal 7a can be stepped downwards by a user's foot so that the chain 8a drags the hub 5a to turn to drive the upper end of the hammer 6a to strike the face of the bass drum to generate drum sound.
Referring to FIG. 2, the drum rim a of the bass drum usually has an elastic protection pad b attached thereon for protection. This increases the clamping distance between the pressing jaw 11a and the base board 2a. And the pressing bolt 12a is screwed in a screw hole of the clamping means 9a at another end at a shorter distance. FIG. 3 illustrates another conventional approach for a thinner drum rim a. The pressing jaw 11a directly compresses and clamps the drum rim a incorporating with the base board 2a. The clamping means 9a is tilted upwards at the rear side and the pressing bolt 12a extends downwards out of the screw hole at a greater distance after screwing into the clamping means 9a. To suit varying thickness of the drum rim a, the length of the pressing bolt 12a has to be made longer. But the longer pressing bolt 12a creates a concern of butting the pedal 7a at the top. Moreover, in the event that a drummer wants to tighten the pressing bolt 12a, his/her hand has to reach into the narrow space beneath the pedal 7a to fumble and wrench the pressing bolt 12a. It is a troublesome operation.
In addition, as shown in FIG. 1, the bass drum usually is positioned at a slight tilted angle in front of the hammer seat 1a. The extent of the tilted angle depends on the preference of the drummer. As a result, the drum rim a also is clamped by the pressing jaw 11a and the base board 2a in a tilted manner. When the hammer strikes the drum face, the drum rim a is subject to a torsional force. This results in warp and deformation of the drum rim a after a period of time in use.